In the semiconductor device manufacturing process, masks are commonly used to define a pattern on a substrate or layer. For example, a mask may be formed using a material that is resistant to etchants so that the underlying substrate or layer is removed during etching where there are gaps in the mask. Alternatively, a mask may be made using a photoresist material that is impervious to radiation (such as ions used during ion implantation) to prevent the areas of the substrate or layer covered by the mask from being penetrated by the radiation.
One particular problem associated with typical photoresist layers used for ion implantation is that they are subject to degradation as a result of high-current, high-dosage, high-energy implants. That is, during implantation bonds within the polymer used to form the photoresist layer are broken, which leads to gases such as H.sub.2, H.sub.2 O, O.sub.2, and N.sub.2 being released from the carbon chain and becoming trapped beneath carbonized photoresist material which is left behind. Stated alternatively, solvents and water present in the photoresist material may cause such gases to form under the carbonized photoresist material during the ion implantation. The formation of these gases results in bubbles which may cause blistering, peeling, lifting, and reticulation of the photoresist layer. Additionally, this problem may be particularly acute in thick photoresist layers, which are used for blocking high-current, high-dosage, high-energy ion implants, for example.
Typical methods for dealing with the above problem include performing an extended hardbake of the photoresist or using a hard mask instead of a photoresist layer. These methods may be disadvantageous because they require longer processing times and/or provide less desirable results than a photoresist layer. A method for enhancing heat resistance and plasma resistance of a photoresist layer is disclosed in U.S. Pat. No. 4,882,263 to Suzuki et al. entitled "Method for Treating Photoresists." The method involves applying ultraviolet rays to a developed photoresist layer at lower than 1 atmosphere of pressure while filtering unwanted radiation from the photoresist to prevent the generation of gases in the photoresist. Yet, to implement such filtering and processing at desired pressure levels may be cumbersome and require additional processing time.
Another prior art method for addressing image flow problems encountered in reactive ion etching processes is disclosed in an article by Hiraoka, H. et al. entitled "UV Hardening of Photo- and Electron Beam Resist Patterns," J. Vac. Sci. Technol., 19(4), November/December 1981, pp. 1132-1135. The article discloses the use of UV exposure or very low heating of resist patterns in air to render images resistant to image flow. Yet, the article fails to address how to alleviate the above-referenced gases to thereby reduce the occurrences of blistering, peeling, lifting, and reticulation.